Real-space imaging of the CO-induced (1 × 2) reconstructions of Pd(011) and (113)

Gaussmann, A.; Kruse, Norbert

doi:10.1016/0039-6028(92)90558-n

Cited by 23 publications

(5 citation statements)

References 30 publications

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“…However, the reconstructed Pd͑110͒͑1 ϫ 2͒ stabilized by oxygen is converted into the ͑1 ϫ 1͒ form when the surface oxygen is removed above 355 K. 43 The ͑1 ϫ 2͒ reconstruction by CO appears only at high CO coverage. [49][50][51][52] LEED observations were consistent with the absence of bidirectional CO 2 desorption in N 2 O or NO reduction. The LEED pattern due to c͑2 ϫ 4͒-O or ͑2 ϫ 3͒-1D-O was suppressed with increasing CO pressures, yielding more products.…”

Section: B Intermediate Structuresupporting

confidence: 72%

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

Matsushima

Shobatake

et al. 2006

The Journal of Chemical Physics

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The angular and velocity distributions of desorbing product N 2 were examined over the crystal azimuth in steady-state NO + CO and N 2 O + CO reactions on Pd͑110͒ by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N 2 desorption in both reactions splits into two directional lobes collimated along 41°-45°from the surface normal toward the ͓001͔ and ͓001͔ directions. Above 600 K, the normally directed N 2 desorption is enhanced in the NO reduction. Each product desorption component, as well as CO 2 , shows a fairly asymmetric distribution about its collimation axis. Two factors, i.e., the anisotropic site structures and the reactant orientation and movements, are operative to induce such asymmetry, depending on the product emission mechanism.

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Section: B Intermediate Structuresupporting

confidence: 72%

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

Matsushima

Shobatake

et al. 2006

The Journal of Chemical Physics

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“…The CO-saturated surface (θ CO = 1.0) gave a peak of ν(CO) at 2003 cm -1 and a (2 × 1)-p2mg LEED pattern. On the other hand, adsorption of CO at 300 K showed completely different spectra 9-11 due to a missing-row type (1 × 2) reconstruction of Pd substrate induced by CO adsorption (0.3 < θ CO < 0.75). − The maximum coverage of CO in UHV at 300 K was 0.75 monolayer (ML) showing a (4 × 2)−CO structure on the (1 × 2) reconstructed substrate …”

Section: Resultsmentioning

confidence: 99%

CO Adsorption and Oxidation on Pd(110)-c(2 × 4)−O by Reflection−Absorption Infrared Spectroscopy

1996

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Adsorption and oxidation of CO on Pd(110)-c(2 × 4)-O were investigated by reflection-absorption infrared spectroscopy (RAIRS), low-energy electron diffraction (LEED), and temperature-programmed reaction (TPR). High-frequency CO at 2140 cm -1 , which was greatly influenced by adsorbed oxygen atoms, was observed by RAIRS even at low CO coverage when the Pd(110)-c(2 × 4)-O surface was exposed to CO at 100 K. This peak developed along with a broad band around 2000 cm -1 from low CO coverage to the saturation. The reaction of CO and an oxygen atom to form CO 2 on the c(2 × 4)-O surface was observed in the range 100-450 K. Below 250 K, two desorption peaks of CO 2 were observed in TPR spectra and the corresponding RAIR spectra showed that linear CO species (2140-2070 cm -1 ) disappeared by desorption as CO or reaction with an oxygen atom to form CO 2 , while there was little decrease of bridge CO species (2020-1880 cm -1 ). It is likely that linear CO species mainly reacted to form CO 2 on Pd(110)-c(2 × 4)-O below 250 K. We successfully followed the constant-flow reaction of CO and O 2 on the Pd(110)-c(2 × 4)-O at 220 K; however, the reaction ceased with an increase of bridge CO at 1992 cm -1 . RAIR spectra during the reaction of CO and O above 250 K suggest that CO began to form domains separated from oxygen atoms and the substrate structure of (1 × 2) was gradually converted into (1 × 1) according to the local coverage of CO. IntroductionOxidation of carbon monoxide on palladium surfaces has been one of most studied subjects over years, which is relevant to a fundamental issue of metal catalysis. 1 Ertl et al. 2,3 have shown that the reaction proceeds via a Langmuir-Hinshelwood mechanism involving adsorbed CO and atomic oxygen. On Pd(100) and Pd(111) surfaces, adsorbate-adsorbate interaction plays an important role in the mechanism. Conrad et al. 3 studied interaction of coadsorbed CO and oxygen on Pd(111) by means of low-energy electron diffraction (LEED), temperatureprogrammed desorption (TPD), and ultraviolet photoelectron spectroscopy (UPS). After preadsorption of oxygen to saturation, a small amount of postdosed CO caused a compression of the oxygen phase and additional CO was adsorbed in domains separate from the oxygen domains. Prolonged exposure to CO produced a coadsorbed phase in which CO and O were in intimate contact. This last phase was extremely reactive for the mutual interaction. Engel and Ertl 2 showed that compression of adsorbed oxygen by CO was responsible for an induction period in their molecular beam oxidation experiments. Stuve et al. 4 studied the interaction of CO and O on Pd(100) by highresolution electron energy loss spectroscopy (HREELS). They reported that CO adsorbed in a compressed islands resulted in the formation of a CO-Pd-O complex with the direct interaction characterized by a CO stretching frequency of 2125 cm -1 . This complex gives CO 2 at a lower temperature below 300 K.Matsushima et al. [5][6][7][8] reported five desorption peaks of CO 2 in the range 150-460 K from CO and dis...

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“…Further adsorption forces them to arrange into regular layers that get compressed at high coverages ,,,− with the appearance of domain walls and show a tendency for the formation of a close-packed layer with a saturation density that is nearly unaffected by the nature of the substrate surface and its crystallographic orientation. , Depending on conditions, a CO molecule may be attached to one, two, or three Pd atoms, ,,,,,,,− which has also been supported by ab initio quantum chemical calculations. − ,, The adsorption energy depends slightly on the crystal planes ,,,− as well as on the CO coverageit is lower at high coverages due to the repulsion among adsorbed CO molecules. ,,,,,, Smaller Pd supported particles (smaller than 5 nm) produce higher CO binding sites, which may be explained by the high participation of edge sites on smaller particles compared with larger ones . Bridged adsorbed species are more firmly bound than uppermost ones. ,,− The adsorption of CO may also induce reconstruction of the Pd surface. ,− …”

Section: Introductionmentioning

confidence: 83%

“…31,39,[45][46][47] The adsorption of CO may also induce reconstruction of the Pd surface. 61,[68][69][70] Adsorption of oxygen to the Pd surface has also been intensively studied using a wide variety of techniques. In summarizing the results we may conclude that oxygen adsorbs molecularly at low temperatures (150 to 200 K) and dissociatively at higher temperatures.…”

Section: Introductionmentioning

confidence: 99%

Carbon-13 Kinetic Isotope Effects in the Catalytic Oxidation of Carbon Monoxide Over Pd/Al₂O₃

1997

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The C-13 kinetic isotope effects in the oxidation of CO by oxygen over a 0.5% Pd/γ-Al2O3 catalyst were experimentally determined in a temperature range of 323−413 K, and the following temperature dependence was found: 100 ln(k 12/k 13) = 3.18−831/T (±0.15). A reaction gas mixture of CO/O2 at a ratio of 1:2 and an initial pressure in a static system ranging from 5 to 10 kPa were used. The reaction kinetics were found to be of order +1 in CO, order 0 in oxygen, and order −1 in CO2. Under these experimental conditions, an activation energy of 56 ± 3 kJ mol-1 was obtained. Using Bigeleisen's formalism based on the absolute rate theory of chemical reactions, kinetic isotope effects were calculated. For the transition state of the rate-determining step, a (CO2)⧧ of various geometries and force constants was considered. The experimental data can be satisfactorily interpreted only with an interbond angle close to 110° and a reaction coordinate described by an asymmetric normal vibration of an asymmetric transition state.

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Real-space imaging of the CO-induced (1 × 2) reconstructions of Pd(011) and (113)

Cited by 23 publications

References 30 publications

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

CO Adsorption and Oxidation on Pd(110)-c(2 × 4)−O by Reflection−Absorption Infrared Spectroscopy

Carbon-13 Kinetic Isotope Effects in the Catalytic Oxidation of Carbon Monoxide Over Pd/Al₂O₃

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Real-space imaging of the CO-induced (1 × 2) reconstructions of Pd(011) and (113)

Cited by 23 publications

References 30 publications

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110)

CO Adsorption and Oxidation on Pd(110)-c(2 × 4)−O by Reflection−Absorption Infrared Spectroscopy

Carbon-13 Kinetic Isotope Effects in the Catalytic Oxidation of Carbon Monoxide Over Pd/Al2O3

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Carbon-13 Kinetic Isotope Effects in the Catalytic Oxidation of Carbon Monoxide Over Pd/Al₂O₃